Satellites are used in a variety of diverse fields such as for navigation, communication, environmental monitoring, weather forecasting, broadcasting and the like. Many homes, businesses, government organizations and other users may use satellites on a daily basis for entertainment, communication, information gathering and other purposes. Hundreds of man-made satellites now orbit the earth, and more are launched each year.
A typical modern satellite may include a metal or composite frame that carries one or more antennas, a power source such as solar cells, and various electronic components. The electronic components on a satellite may include one or more transponders. The transponders may be clusters of electronic components including one or more receivers, frequency translators and transmitters. Each transponder may be configured for a particular bandwidth. The total bandwidth of the satellite may be provided by the number of transponders.
The transponders on a communications satellite may be configured to receive multiple uplink beams from the earth, another satellite, or other stationary or mobile locations via uplink antennas. Each of the received beams may be amplified and down-converted for further processing by the transponders. The down-converted beams then may be switched, multiplexed or otherwise routed and combined prior to up-conversion and re-transmission on a downlink beam to the earth, other satellite, or other stationary or mobile location via a downlink antenna.
The transponders on a communications satellite may be analog or digital. For analog transponders, switching may be limited to point-to-point mapping of entire uplink antenna beams to particular downlink antenna beams. A digital transponder on a communications satellite may provide the functionality of the transponder using digital signal processing. A digital transponder may be configured to divide, control and monitor bandwidths and power allocations for communications signals onboard the satellite in a manner that may not be achieved with an analog transponder.
A digital transponder may have the ability to perform switching of inputs to outputs in a highly flexible manner. A number of transponders employ a switch including a multiple stage switch network such as a Clos switch network with multiple stages of switches through which paths or connections may be made between inputs and outputs. And some of these multiple stage switch networks are rearrangeable non-blocking (RANB) in that an idle input may always be connected to an idle output without disrupting other existing connections between inputs and outputs (non-blocking) and through one or more stages of switches therebetween, but doing so may require rearranging one or more existing connections (rearrangeable).
In instances in which a connection through a multiple stage switch network is rearranged, it is often desirable if not required that the process of rearranging the connection does not cause any outage (lost data, “hitless”) in traffic over the connection. Conventional networks accomplish this by setting up a redundant connection between the connection's input and output (make-before-break), but this undesirably increases the complexity of the algorithm according to which the network and connections through the network are controlled. And building in an allowance for redundant connections undesirably reduces the capacity of the switch network.
Accordingly, it would be beneficial to have a method and apparatus that takes into account one or more of the issues discussed above as well as possibly other issues.